Thesis from Leicester PolytechnicAcer pseudoplatanus L (English sycamore) cell suspension cultures provide an excellent system for controlled investigations into the regulation of cytokinesis. They exhibit 60-70% division synchrony on subculture, and produce predictable growth patterns in batch culture.
Previous studies in these laboratories with partially synchronized cultures led to the hypothesis that a critical "trigger" concentration of endogenous IAA (approximately 500-750 ng 10 8 cells) is vital prior to each mitosis. In this present study a more effective induction technique has been employed. The cells were found to rapidly become nitrate and phosphate limited in
batch culture. The addition of these nutrients after each cell division resulted in several highly synchronous divisions (80-90%). In"these cultures 'the IAA levels remained at a relatively stable level (50 ng 108 cells). Thus, the original hypothesis has been
modified and it is now proposed that a critical minimum endogenous concentration of IAA is required to maintain
cytokinesis. This IAA level may be optimal for an IAA binding protein.
The nutrient feeding system was adapted for automation with the aid of a computer Interface. This automated system ensures,-- that the synchronization technique is more reliable and less time consuming.
The endogenous cytokinins were studied during the first cell division. The individual levels were found to fluctuate with total cytokinin-like activity reaching a maxima -coincident with mitosis and/or cytokinesis. Z was the major cytokinin detected. This implicated the cytokinins as possible G2 --) M triggers.
The Intracellular pH levels were estimated by 31p NMR spectroscopy. The cytoplasmic pH remained stable (approximately 7.5) during synchronous divisions and decreased as asynchrony developed. This may be a reflection of the nutrient status of the cells and/or the level optimal for"the distribution of IAA and/or other growth regulators.
The cell cycle appears to be controlled by the various growth regulators and their receptors. It is apparent that the concentrations, availability and distribution of these substances is vital for the complex regulated cycle to ensue
